The problem is that in Total Commander a default editor can de defined for the F4 key, but not on a file extension basis, so you will end up using a generic text editor and get used to it for any kind of text file.

Here I will describe some ways to provide quick access to AutoGUI.

Before you start, copy the full path of AHK and AutoGUI, because there are some modal dialogs further on.1. Define the F12 key to open the selected files in AutoGUI.
Steps:
• Go to Configuration > Options > Misc.
• In "Redefine hotkeys", select F12 (or any other key combination not in use) in the drop-down list.
• Click the magnifying glass button to open the "Choose command" dialog.
• Scroll the category list (the left panel) to the bottom and select "usercmd.ini".
• Click the button "New" and type in "em_AutoGUI". Click OK.
• A dialog will open. Fill in the following parameters:
Command: "C:\PATH\TO\AutoHotkey.exe"
Parameters: "C:\PATH\TO\AutoGUI.ahk" %P%S10
Icon file: "C:\PATH\TO\AutoGUI\Icons\AutoGUI.icl"
• Click OK, OK and OK. Now you can press F12 to open the selected files in AutoGUI.2. Create a toolbar button for AutoGUI.
Steps:
• Go to Configuration > Button Bar... (or right-click an empty area of the toolbar and select "Change...").
• Click "Add".
• Fill in the same parameters described above (unless you already added "em_AutoGUI" to usercmd.ini, in which case simply select it from the list of commands).
• Press OK. Clicking the toolbar button now opens the selected files in AutoGUI.3. Create a script to filter the file extension and set it as default editor for F4.

This is the case if you are interested in defining specific programs as editors for different file types. There's already a tool written in AHK for this (I have not tested it yet): F4MiniMenu.
And of course you can use the Explorer context menu in Total Commander. At some point I will provide a utility to set the registry association (AutoGUI as default AHK editor) and Start menu shortcuts for AutoGUI and its tools.

Alguimist wrote:3. Create a script to filter the file extension and set it as default editor for F4.
This is the case if you are interested in defining specific programs as editors for different file types. There's already a tool written in AHK for this (I have not tested it yet): F4MiniMenu.